Optimizing Perovskite Solar Cell Efficiency with Size‑Controlled Ag Nanoparticles in a TiO₂ Compact Layer

Abstract

Silver (Ag) nanoparticles (Ag NPs) of controlled size and concentration were incorporated into a TiO₂ compact layer via a polyol synthesis route to enhance the performance of perovskite solar cells (PSCs). X‑ray diffraction confirmed that the anatase TiO₂ lattice remained unchanged after Ag addition, while transmission electron microscopy revealed that Ag NP size directly influences the light‑harvesting capacity of the perovskite absorber. We found that 10‑nm Ag NPs at a 1.5 mol % (Ag:Ti) loading deliver the highest power‑conversion efficiency (PCE) of 13.26 %, attributed to accelerated charge transfer, reduced recombination, and amplified visible‑light absorption.

Background

Perovskite solar cells have surged from a 3.8 % to a 22.1 % PCE in the last decade, owing to their direct bandgap, high carrier mobility, and strong absorption coefficients. In planar PSC architectures, a compact TiO₂ layer acts as a hole‑blocking barrier, while a mesoporous TiO₂ or ZrO₂ scaffold provides a high‑area interface for perovskite deposition. Nanostructured metals, especially Ag and Au, exhibit localized surface plasmon resonance (LSPR) that can boost the optical absorption of adjacent semiconductors. Although plasmonic PSCs have been reported, the specific impact of Ag NPs embedded in a TiO₂ compact layer has remained underexplored.

Methods

Ag NPs of 10, 30, 40, and 55 nm diameters were synthesized by reducing AgNO₃ in ethylene glycol with polyvinylpyrrolidone (PVP, K30) at 120–150 °C. The resulting colloids were washed and dried to yield monodisperse particles. TiO₂ precursor solutions (1 ml titanium isopropoxide bis(75 %) in 19 ml ethanol) were mixed with Ag NPs to achieve 0.5–2.5 mol % Ag:Ti ratios and stirred for 1 h. FTO‑glass substrates were sequentially coated with the Ag‑doped TiO₂ compact film (4000 rpm, 20 s; 150 °C, 10 min; 500 °C, 30 min), then annealed at 500 °C for 30 min. A mesoporous TiO₂/ZrO₂ layer was deposited by spin‑coating a 1:5 TiO₂/ZrO₂ colloid, followed by the perovskite FA₀.₄MA₀.₆PbI₃ layer (spin‑coating at 1000 rpm/10 s, 4000 rpm/30 s; 1 ml diethyl ether added; 100 °C, 10 min). Carbon counter electrodes (30 µm) were screen‑printed and annealed at 100 °C for 30 min.

Structural characterization employed FE‑SEM, TEM, XRD, and XPS. Device performance was measured under AM 1.5G (100 mW cm⁻²) illumination, and UV‑vis spectra were recorded to assess absorption. Incident photon‑to‑electron conversion efficiency (IPCE) was determined using a Newport 300 W xenon lamp.

Results and Discussion

TiO₂ XRD patterns remained anatase regardless of Ag inclusion, confirming structural integrity. XPS showed Ag 3d peaks at 368.3 and 374.3 eV, indicating metallic Ag with no chemical reaction. TEM images verified monodisperse Ag NPs and uniform dispersion within the TiO₂ matrix.

UV‑vis spectra revealed that the plasmonic absorption peak shifts from ~400 nm (10 nm NP) to ~420 nm (55 nm NP). Smaller Ag NPs exhibited stronger LSPR and higher absorption in the visible region, leading to enhanced photogeneration in the perovskite layer. As Ag content increased, absorption intensified up to 2.5 mol %, but excessive loading introduced charge‑trapping sites that diminished performance.

J‑V measurements showed that all Ag‑doped devices maintained similar open‑circuit voltages (≈1.0 V) while achieving higher short‑circuit currents. The 10‑nm Ag NPs at 1.5 mol % achieved a PCE of 13.26 %, outperforming the pristine device (12.08 %) and other size/concentration combinations. IPCE spectra confirmed that the 10‑nm NP device exhibited the largest enhancement across 380–780 nm, corroborating the LSPR‑induced absorption benefit.

Conclusions

Incorporating 10‑nm silver nanoparticles at a 1.5 mol % loading into a TiO₂ compact layer optimally balances plasmonic absorption and charge transport, raising PSC efficiency to 13.26 %. These findings provide a clear pathway for tailoring nanoparticle size and concentration to maximize perovskite device performance.